An image processing apparatus having improved detection performance for detecting an abnormal shadow, such as a tumor, and reducing a burden on the user is disclosed. In the image processing apparatus, an aligning unit aligns a previous image and a current diagnosis image with each other, and a corresponding position calculating unit calculates a position on a subject in the current diagnosis image corresponding to the position of an abnormal shadow on the subject in the previous image based on positional information of the abnormal shadow on the subject in the previous image and alignment information. A current diagnosis image abnormal shadow detecting unit detects the abnormal shadow in the current diagnosis image from the vicinity of the corresponding position in the current diagnosis image.